1. Field of the Invention
This invention generally relates to a diversity receiver, and more particularly concerns the diversity receiver for communication by radio-wave, for instance, between a sensor part and a main controller part in a security system and the like.
2. Description of the Prior Art
For instance in a home security system to be used in a usual home, a transmitting and a receiving system for communicating between very short distances has used a low power radio-wave. When a weak or unstable radio-wave signal is received, a part of the signals are likely to disappear under influence of interference by reflection or other causes. In order to prevent such missing portions of the signals, a diversity receiver system has been adopted. Especially in the field of communication of information in a security system, a high reliability is required.
The prior art diversity receiving system is shown in FIG. 12. The prior art diversity receiving system to be used for such object has been constituted to receive a radio-wave which is modulated by the security information by using plural antennas 3, 4 and plural receivers 5, 6 for respective antennas 3, 4. Signals received by each antenna 3, 4 are amplified, converted of its frequency and is filtered by a filter means. Thus, plural output signals are obtained. Intensities of the plural output signals are compared with each other by the comparator 7, and the strongest output signal is selected by a switch 8. The selected signal is demodulated by a demodulator 9, and the information which is contained in the signal is decoded by a decoder 10. This information is displayed or used to control some apparatus. The above-mentioned conventional diversity receiver selects the strongest signal among those the plural antennas have received. Since the plural antennas are set up keeping predetermined distances from each other, a probability that all the signals from the plural antennas are simultaneously attenuated is little, and hence a high reliability receiving is assured.
Nevertheless, the above-mentioned conventional system has a shortcoming in that it requires plural receivers 5, 6. Since each receiver 5, 6 has a complicated circuits, such receivers 5, 6 with plural receiving system is, not only expensive, but also big in size, and consumes much electric power. Furthermore, it is a shortcoming that switching noises is likely to be introduced at switching of the plural receivers 5, 6.